Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
The trend in pixel development toward smaller photodiodes and detection of longer absorbed wavelengths necessitates enhanced optical and electrical isolation between individual photodiodes. To improve isolation many approaches have been suggested; all of these approaches consume valuable real estate on the image sensor wafer. The area of each pixel generally consists of isolation structures, photodiodes—which, preferably, are made as large as possible—and accompanying in-pixel transistors necessary for imager operation. Area consumed by isolation and in-pixel transistors is likely not available for photodiodes. Thus, minimizing isolation and transistor regions is desirable to maximize photodiode area.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.